Misalignment and Resonance Torques and Their Treatment in the GP-B Data Analysis

Classical torques acting on the GP-B gyroscopes decrease the accuracy in the measurement of the relativistic drift rate. Based on measurements made during the year-long science data collection, tests done following the science data collection, and a theoretical analysis of potential torques, there are two dominant classical torques acting on the gyroscopes. The first torque, known as the misalignment torque, has a magnitude proportional to the misalignment between the gyroscope spin axis and the satellite roll axis and is aligned perpendicular to the plane containing these two vectors. The second torque, known as the resonance torque, mainly produces a permanent offset in the orientation of the gyroscope spin axis when a harmonic of the gyroscope polhode frequency is in the vicinity of the satellite roll frequency. These two torques have the same physical origin: an electrostatic interaction between the patch effect fields on the surfaces of the rotor and the housing. In the post-mission data analysis, the change in the gyroscope orientation due to both of these torques can be clearly separated from the relativistic drift rate.